Lipids are a family of naturally occurring amphiphilic small molecules. Representative examples of lipids include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, and phospholipids. The removal or capture of lipids from within various compositions finds application in a broad range of fields including food processing, medicine development, and chemical analysis.
Within each field, a variety of existing methods for capturing or removing lipids from a composition may be used depending on the particular composition, including thermal rendering, skimming, supercritical fluid extraction, solvent extraction, liquid-liquid extraction (LLE), and solid phase extraction (SPE). Depending on the intended use for the particular composition, a number of constraints on the method of lipid extraction and choice of reagents selected to carry out the lipid removal may be considered. Thermal rendering and skimming are economical methods of removing lipids from a composition, but these non-specific removal methods may unintentionally eliminate desirable non-lipid compounds from the composition, or the high temperatures of these methods may alter or damage the remaining compounds in the composition. Supercritical fluid extraction may also have similar disadvantages such as the non-specific extraction of lipid compounds as well as potentially damaging process conditions. Solvent extraction and liquid-liquid extraction are more selective lipid removal methods that may have less adverse effects on other compounds in the composition, but may also produce large volumes of solvent waste. SPE is another existing method of selectively removing lipids from a sample with minimal adverse effects on other compounds in the composition, while generating significantly lower amounts of waste solvents and other waste reagents compared to solvent extraction or liquid-liquid extraction methods.
SPE methods are based on contacting the composition with a solid phase adsorbent that has a selective affinity for lipids, and then separating the remaining lipid-free composition from the adsorbent. The adsorbent compositions used to immobilize the lipids in existing SPE methods are typically one of two types. The first adsorbent composition, typically used for immobilizing the phospholipid subset of the lipids includes a transition metal oxide such as titania, ceria, or zirconia, as described in US published application US2008/0213906, the contents of which are hereby incorporated by reference in entirety. A second type of adsorbent composition currently used for the capture or removal of lipids such as triglycerides include hydrophobic alkyl moieties or hydrophobic filtration materials such as PVDF membranes or frits.
The SPE compositions currently used for lipid removal have proven to be ineffective at removing more than a limited subset of the lipids, due to the wide range of chemical characteristics of the various lipid types. The transition metal oxide moieties of the first type of adsorbent composition are effective at binding polar moieties of certain lipids such as the phosphate groups of single-chain phospholipids, but are less effective at binding lipids with a higher proportion of nonpolar moieties such as the dual-chain phospholipids that include two nonpolar long-chain hydrocarbon moieties. The hydrophobic alkyl moieties of the second adsorbent composition type are effective at binding lipids possessing larger proportions of nonpolar long chain alkyls such as triglycerides, but are less effective at binding monoglycerides, which have a lower proportion of nonpolar alkyl chains.
A need exists for an SPE media composition that is effective at selectively capturing a wide range of lipid types that may include polar and nonpolar moieties in various proportions from a sample that may also contain other compounds such as target analytes that are of interest to the pharmaceutical sciences, environmental testing, and food science. In addition, a need exists for an SPE media composition that captures a wide range of lipid types in a sample that may contain additional compounds such as protein precipitation agents that may influence the chemical properties of the sample. Further, a need exists for an SPE media composition that is effective at selectively capturing a wide range of lipid types without capturing a variety of acidic, nonacidic and neutral target analytes.